A metal compound coating, a preparation method thereof, and a modified bipolar plate

Abstract

The present invention relates to the technical fields of water electrolysis devices, bipolar plates, and coating materials, and particularly relates to a metal compound coating, a preparation method thereof, and a modified bipolar plate. The metal compound coating is used to cover the surface of the bipolar plate of the water electrolysis device. The preparation method of the metal compound coating includes the following steps: using the bipolar plate of the water electrolysis device as a substrate, depositing a titanium nitride coating on the surface of the substrate by a pulsed laser deposition process; then, using a plasma surface oxygen permeation process to perform oxygen permeation on the titanium nitride coating to form a titanium oxynitride coating with a gradient change in oxygen content. The present invention mainly uses pulsed laser deposition technology and plasma oxygen permeation technology to generate a titanium oxynitride coating with a gradient change in oxygen content on the surface of the titanium bipolar plate, which has both corrosion resistance and conductivity, and solves the problem that the existing composite coating preparation method causes the protective performance of the coating to decline due to interface defects and stress concentration between different coatings, affecting the long-term stability of the coating.

Description

Technical Field

[0001] The present invention relates to the technical fields of water electrolysis devices, bipolar plates and coating materials, and particularly relates to a metal compound coating, a preparation method thereof and a modified bipolar plate. Background Art

[0002] The full English name of proton exchange membrane water electrolysis is Proton Exchange Membrane Water Electrolyzers, abbreviated as PEMWE. The proton exchange membrane is abbreviated as PEM. The proton exchange membrane water electrolysis hydrogen production technology has the advantages of fast response speed, low operating temperature, high current density, high hydrogen production purity and environmental friendliness. Therefore, the PEM electrolytic water hydrogen production technology has attracted much attention in the field of hydrogen energy production. In the water electrolysis technology, as a key component of the PEM water electrolyzer, the bipolar plate mainly functions to collect current, support the membrane electrode assembly, uniformly transfer reaction media, conduct electricity and heat, etc. Therefore, it is required that the bipolar plate must have certain mechanical strength, good corrosion resistance, good thermal conductivity, good processability and other properties.

[0003] At present, metal bipolar plates have become the first choice for commercial bipolar plates due to their superior mechanical properties. Among them, titanium bipolar plates have good mechanical strength, good processability and good corrosion resistance. However, in the strongly corrosive working environment of the PEM water electrolyzer, an oxide film is likely to form on the surface of the titanium bipolar plate, increasing the interfacial contact resistance with the gas diffusion layer; in addition, the titanium bipolar plate may corrode, releasing metal ions, which may cause poisoning of the catalyst and the proton exchange membrane, affecting the service life of the electrolyzer.

[0004] At present, the key to improving the performance of titanium bipolar plates lies in the optimization technology of their surface coatings. Studying a coating with both high conductivity and high corrosion resistance to improve the performance of titanium bipolar plates has become the main research direction at present. Traditional coating preparation methods mostly adopt multi-layer functional layer composite technology, aiming to comprehensively improve corrosion resistance and conductivity through the functional superposition of different coatings. For example, the patent application with the publication number CN114214658A proposed an innovative composite coating preparation method. This method selects TA1 type pure titanium as the metal bipolar plate substrate, enhances the adhesion of the substrate surface through pretreatment, and then alternately deposits a self-healing layer and a corrosion-resistant layer on it in sequence to form a bottom layer structure with self-repair ability and strong corrosion resistance. Finally, a conductive layer is deposited on the outermost corrosion-resistant layer to ensure the good electrical conductivity of the bipolar plate.

[0005] However, although this multi-layer coating structure can theoretically balance corrosion resistance and conductivity, it faces many challenges in practical applications. For example, the performance differences between different coatings may lead to a weakened interfacial bonding force, which in turn affects the overall stability and service life of the coating. The preparation process of the multi-layer coating is complex and requires precise control of the deposition parameters and thickness of each layer to ensure good matching and synergistic effects between the coatings. In addition, due to the physical and chemical property differences between the coating materials, there are often interface defects and stress concentration problems between the multi-layer coatings. These problems may become breakthrough points for the erosion of corrosive media, resulting in a decline in the protective performance of the coating.

[0006] Specifically, for the sample prepared in the patent application with the publication number CN114214658A, although the corrosion resistance and conductivity of the titanium bipolar plate are improved to a certain extent, its corrosion current density is still as high as 2.5×10 −6 A·cm −2 , which indicates that there is still a certain corrosion risk for the coating under long-term and high-load electrolytic environments. Summary of the Invention

[0007] In order to solve the problem that the existing composite coating preparation method leads to a decline in the protective performance of the coating due to interface defects and stress concentration between different coatings, affecting the long-term stability of the coating, the purpose of the present invention is to provide a metal compound coating, its preparation method, and a modified bipolar plate.

[0008] To achieve the above purpose, the technical solution of the present invention is as follows.

[0009] In the first aspect of the present invention, a preparation method of a metal compound coating is provided. The metal compound coating is used to cover the surface of the titanium bipolar plate of a water electrolysis device. The preparation method of the metal compound coating includes the following steps:

[0010] Using the titanium bipolar plate of the water electrolysis device as a substrate, a titanium nitride coating is deposited on the surface of the substrate by a pulsed laser deposition process; then, a plasma surface oxygenation process is used to oxygenate the titanium nitride coating to form a titanium oxynitride coating with a gradient change in oxygen content.

[0011] The present invention mainly uses pulsed laser deposition technology and plasma oxygenation technology to generate a titanium oxynitride coating with a gradient change in oxygen content on the surface of the titanium bipolar plate. While maintaining high corrosion resistance, it also has good conductivity, no noble metal loading, and low cost, solving the problem that the existing composite coating preparation method leads to a decline in the protective performance of the coating due to interface defects and stress concentration between different coatings, affecting the long-term stability of the coating.

[0012] The method of the present invention adopts a plasma oxygen permeation process to form a titanium oxynitride gradient coating structure, where the oxygen content varies with the coating thickness. The oxygen content on the coating surface is high, and the oxygen content decreases near the titanium substrate, enabling the coating to achieve both corrosion resistance and conductivity. This is mainly because the corrosion resistance of titanium dioxide is better than that of titanium nitride. Therefore, the oxygen content is increased on the basis of the titanium nitride coating to improve the corrosion resistance of the titanium oxynitride coating. However, when the oxygen content is too high, the conductivity of the titanium oxynitride coating will decrease. Therefore, the present invention adopts a plasma oxygen permeation process to form a titanium oxynitride gradient coating structure to improve the corrosion resistance while maintaining a certain conductivity.

[0013] Preferably, for the titanium oxynitride coating, the oxygen content gradually decreases along the thickness direction, and the oxygen content of the titanium oxynitride coating gradually approaching the substrate decreases.

[0014] The titanium oxynitride coating of the present invention is a gradient coating, and its oxygen content varies with the coating thickness. The oxygen content on the coating surface is high, and the oxygen content decreases near the titanium substrate.

[0015] Preferably, the thickness of the titanium oxynitride coating with a gradient change in oxygen content is 240 nm to 300 nm.

[0016] Preferably, the method for depositing a titanium nitride coating on a substrate by pulsed laser deposition technology includes the following steps:

[0017] Using a pulsed laser deposition process, with a TiN target as the target material and nitrogen as the working gas, nitrogen is introduced after the vacuum degree reaches <2×10 −4 Pa, and a titanium nitride coating is formed on the substrate surface.

[0018] Preferably, the conditions of the pulsed laser deposition process are:

[0019] The pulse frequency is 8 Hz to 10 Hz, the laser energy is 400 mJ to 450 mJ, the gas pressure in the reaction chamber is 8 Pa to 10 Pa, the deposition temperature is 400 °C to 450 °C, and the number of pulsed depositions is 12,000 times to 16,000 times.

[0020] In the present invention, the titanium nitride coating on the substrate is a continuous and dense metal nitride coating, with a golden yellow appearance, and the coating thickness is about 300 nm.

[0021] Preferably, the purity of the TiN target is ≥99.9%. The purity of nitrogen is ≥99.9%.

[0022] Preferably, the method for forming a titanium oxynitride coating with a gradient change in oxygen content includes the following steps:

[0023] The plasma surface oxygen permeation process is adopted. Oxygen is introduced and ionized to form oxygen plasma, which then penetrates into the titanium nitride coating to form a titanium oxynitride coating with a gradient change in oxygen content.

[0024] Preferably, the conditions of the plasma surface oxygen permeation process are as follows:

[0025] The power is 60 W, the temperature is 200 °C to 400 °C, the air pressure in the reaction chamber is 15 Pa to 30 Pa, and the oxygen permeation time is 1 h to 3 h.

[0026] In the plasma oxygen permeation process step of the present invention, by optimizing different process parameters, including oxygen pressure, substrate temperature, oxygen permeation time, etc., a uniform and dense coating is obtained, reducing the influence of surface cracks and ensuring the corrosion resistance of the coating. The self-corrosion current density of the metal compound coating prepared by the present invention can be optimally 6.8×10 −8 A·cm −2 , and at a working voltage of 2.0 V, the corrosion current density is less than 1×10 −7 A·cm −2 ; the interface contact resistance is less than 9 mΩ·cm 2 .

[0027] Preferably, before depositing the titanium nitride coating on the substrate surface by the pulsed laser deposition process, it also includes performing a grinding and polishing pretreatment on the substrate surface to remove the oxide film on the substrate surface and obtain the substrate material.

[0028] The second aspect of the present invention provides a metal compound coating, which is prepared by the preparation method described in the first aspect.

[0029] Preferably, at a working voltage of 2.0 V, the corrosion current density of the metal compound coating of the present invention is less than 1×10 −7 A·cm −2 ; the interface contact resistance of the transition metal compound composite coating is less than 9 mΩ·cm 2 .

[0030] The third aspect of the present invention provides a modified bipolar plate, which includes a substrate and a metal compound coating. The substrate is a titanium bipolar plate for a water electrolysis device, and the metal compound coating is the metal compound coating described in the second aspect.

[0031] The modified bipolar plate of the present invention is used for a proton exchange membrane water electrolysis cell, and a metal compound coating described in the second aspect is deposited on the surface of the titanium bipolar plate for the water electrolysis device.

[0032] The beneficial effects of the present invention:

[0033] 1. The present invention mainly uses pulsed laser deposition technology and plasma oxygen permeation technology to generate a titanium oxynitride coating with a gradient change in oxygen content on the surface of a titanium bipolar plate. While maintaining high corrosion resistance, it also has good electrical conductivity, no noble metal loading, and low cost, solving the problem that the existing composite coating preparation methods lead to a decline in the protective performance of the coating due to interface defects and stress concentration between different coatings, affecting the long-term stability of the coating.

[0034] 2. The method of the present invention uses a plasma oxygen permeation process to form a titanium oxynitride gradient coating structure, where the oxygen content changes with the coating thickness. The oxygen content on the coating surface is high, and the oxygen content decreases near the titanium substrate, enabling the coating to achieve both corrosion resistance and electrical conductivity. This is mainly because the corrosion resistance of titanium dioxide is better than that of titanium nitride. Therefore, increasing the oxygen content on the basis of the titanium nitride coating can improve the corrosion resistance of the titanium oxynitride coating. However, when the oxygen content is too high, the electrical conductivity of the titanium oxynitride coating will decrease. Therefore, the present invention uses a plasma oxygen permeation process to form a titanium oxynitride gradient coating structure to improve corrosion resistance while maintaining a certain electrical conductivity.

[0035] 3. The titanium oxynitride coating prepared by the present invention exhibits better corrosion resistance while maintaining good electrical conductivity, and the coating has good denseness, which can provide good protection for the substrate. The self-corrosion current density of the metal compound coating of the present invention can be optimally 6.8×10 −8 A·cm −2 , which is 1 - 2 orders of magnitude higher than that of the prior art.

[0036] 4. The metal compound coating generated by the present invention has good adhesion to the titanium substrate, and the interfacial contact resistance with the gas diffusion layer is significantly reduced. The modified bipolar plate of the present invention has a corrosion current density of less than 1×10 −7 A·cm −2 at a working voltage of 2.0V; the interfacial contact resistance is less than 9 mΩ·cm 2 , having good electrical conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a SEM image of the cross-section of a titanium bipolar plate sample with a titanium oxynitride coating on the surface in Example 1.

[0038] Figure 2 is a SEM image of the titanium oxynitride coating in Example 1.

[0039] Figure 3 is a schematic diagram of the titanium nitride coating on the surface of a titanium bipolar plate and the titanium oxynitride coating prepared by using a plasma oxygen permeation process in the implementation manner of the present invention.

[0040] Figure 4 It is the XPS depth analysis diagram of the cross-section of the titanium bipolar plate sample with a titanium oxynitride coating on the surface in Example 1. Among them, 0 min to 7 min is the XPS sputtering time.

[0041] Figure 5 It is the potentiodynamic scanning test diagram of the samples of Example 1, Comparative Example 1 and Comparative Example 2.

[0042] Figure 6 It is the contact resistance test diagram of the samples of Example 1, Comparative Example 1 and Comparative Example 2.

[0043] Figure 7 It is the potentiostatic scanning test diagram of the samples of Example 1, Example 2 and Comparative Example 1. Detailed implementation manners

[0044] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0045] Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0046] The present invention mainly uses pulsed laser deposition technology and plasma oxygen infiltration technology to generate a titanium oxynitride coating with a gradient change in oxygen content on the surface of the titanium bipolar plate. While maintaining high corrosion resistance, it also has good electrical conductivity, no noble metal loading, and low cost, solving the problem that the existing composite coating preparation methods lead to a decrease in the protective performance of the coating due to interface defects and stress concentration between different coatings, affecting the long-term stability of the coating. The specific preparation method is as follows:

[0047] A preparation method of a metal compound coating, the metal compound coating is used to cover the surface of the bipolar plate of a water electrolysis device, and the preparation method of the metal compound coating includes the following steps:

[0048] Step 1, pretreatment of the substrate surface: The substrate surface is polished and pretreated to remove the oxide film on the substrate surface to obtain a matrix material.

[0049] Step 2, deposition of a titanium nitride coating on the surface of the titanium substrate: Using the bipolar plate of the water electrolysis device as the substrate, a titanium nitride coating is deposited on the substrate surface by pulsed laser deposition process. The titanium nitride coating on the substrate is a continuous and dense metal nitride coating, with a golden yellow appearance, and the coating thickness is about 300 nm. The specific method is as follows:

[0050] Using the pulsed laser deposition process, with a TiN target as the target material and nitrogen as the working gas, nitrogen is introduced after the vacuum degree reaches <2×10 −4 Pa, and a titanium nitride coating is formed on the substrate surface.

[0051] The conditions of the pulsed laser deposition process are: the pulse frequency is 8 Hz to 10 Hz, the laser energy is 400 mJ to 450 mJ, the air pressure in the reaction chamber is 8 Pa to 10 Pa, the deposition temperature is 400 °C to 450 °C, and the number of pulsed depositions is 12,000 times to 16,000 times. The purity of the TiN target is ≥99.9%. The purity of nitrogen is ≥99.9%.

[0052] Step 3, oxygen infiltration process on the surface of the titanium nitride coating: Then, the plasma surface oxygen infiltration process is used to infiltrate oxygen into the titanium nitride coating to form a titanium oxynitride coating with a gradient change in oxygen content. The oxygen content of the titanium oxynitride coating gradually decreases along the thickness direction, approaching the substrate. The thickness of the titanium oxynitride coating with a gradient change in oxygen content is 240 nm to 300 nm. The specific method is as follows:

[0053] Using the plasma surface oxygen infiltration process, oxygen is introduced, ionized to form oxygen plasma, and then infiltrated into the titanium nitride coating to form a titanium oxynitride coating with a gradient change in oxygen content.

[0054] The conditions of the plasma surface oxygen infiltration process are: the temperature is 200 °C to 400 °C, the air pressure in the reaction chamber is 15 Pa to 30 Pa, and the oxygen infiltration time is 1 h to 3 h.

[0055] The method of the present invention uses the plasma oxygen infiltration process to form a titanium oxynitride gradient coating structure, where the oxygen content changes with the coating thickness. The oxygen content on the coating surface is high, and the oxygen content decreases near the titanium matrix, enabling the coating to achieve both corrosion resistance and conductivity.

[0056] In the plasma oxygen infiltration process step of the present invention, by optimizing different process parameters, including oxygen pressure, substrate temperature, oxygen infiltration time, etc., a uniform and dense coating is obtained, reducing the influence of surface cracks and ensuring the corrosion resistance of the coating.

[0057] The self-corrosion current density of the metal compound coating prepared by the present invention can be optimally 6.8×10 −8 A·cm −2 , and at a working voltage of 2.0 V, the corrosion current density is less than 1×10 −7 A·cm −2 ; the interface contact resistance is less than 9 mΩ·cm 2 .

[0058] The technical solution of the present invention will be further described below through specific embodiments. In the following embodiments, unless otherwise specified, the methods are all conventional methods; unless otherwise specified, the reagents and materials can be obtained in the market.

[0059] Example 1

[0060] As Figure 3 , a method for preparing a metal compound coating on the surface of a titanium bipolar plate, comprising the following steps:

[0061] S1. Surface pretreatment of the titanium substrate: Select a commercial TA1 titanium plate as the titanium substrate, and the commercial TA1 titanium plate is a titanium bipolar plate. Use SiC sandpaper with a particle size of 1000 mesh to 5000 mesh to polish to remove the oxide film on the surface of the titanium bipolar plate. Then, use diamond polishing paste with a particle size of 0.5 µm to polish the surface of the titanium substrate into a mirror state. Ultrasonically clean the polished titanium substrate with absolute ethanol for 30 minutes to remove grease and dirt. Finally, air dry naturally and place it in absolute ethanol for standby.

[0062] S2. Deposition of a titanium nitride coating on the surface of the titanium substrate: Fix the air-dried titanium substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 −4 Pa, introduce high-purity nitrogen, adjust the nitrogen flow rate so that the nitrogen partial pressure is maintained at about 8 Pa; set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 400 mJ, and the number of pulses to 16000 times. Turn on the laser switch to start depositing the titanium nitride coating; obtain a titanium bipolar plate with a titanium nitride coating on the surface.

[0063] S3. Oxygen infiltration process on the surface of the titanium nitride coating: Place the titanium bipolar plate with a titanium nitride coating on the surface prepared by the pulsed laser deposition process in the reaction chamber of the plasma chemical vapor deposition equipment. Raise the substrate temperature to 200 °C. After the chamber vacuum is lower than 1×10 −3 Pa, introduce oxygen into the chamber, adjust the oxygen flow rate so that the oxygen pressure is maintained at 15 Pa. Then turn on the radio frequency power supply, keep the power at 60 W, ionize the oxygen to form a plasma, and infiltrate it into the titanium nitride coating. The oxygen infiltration time is maintained for 1 h to form a titanium oxynitride coating.

[0064] S4. Turn off the radio frequency power supply switch, naturally cool to room temperature, and take out the sample from the chamber.

[0065] Example 2

[0066] As Figure 3 , a method for preparing a metal compound coating on the surface of a titanium bipolar plate, comprising the following steps:

[0067] S1. Surface pretreatment of the titanium substrate: Select a commercial TA1 titanium plate as the titanium substrate, and the commercial TA1 titanium plate is a titanium bipolar plate. Polish it with 1000 - 5000 - mesh SiC sandpaper to remove the oxide film on the surface of the titanium bipolar plate. Then, use diamond polishing paste with a particle size of 0.5 µm to polish the surface of the titanium substrate into a mirror state. Ultrasonically clean the polished titanium substrate with absolute ethanol for 30 min, and finally air - dry it naturally.

[0068] S2. Deposition of titanium nitride coating on the surface of the titanium substrate: Fix the air - dried titanium substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 −4 Pa, introduce high - purity nitrogen gas, and adjust the nitrogen gas flow rate so that the nitrogen partial pressure remains at about 8 Pa; Set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 400 mJ, and the pulse number to 16000 times. Turn on the laser switch to start depositing the titanium nitride coating; Obtain a titanium bipolar plate with a titanium nitride coating on its surface.

[0069] S3. Oxygen infiltration process on the surface of the titanium nitride coating: Place the titanium bipolar plate with a titanium nitride coating on its surface prepared by the pulsed laser deposition process in the reaction chamber of the plasma - enhanced chemical vapor deposition equipment. Heat the substrate temperature to 200 °C. After the chamber vacuum is lower than 1×10 −3 Pa, introduce oxygen into the chamber, and adjust the oxygen flow rate so that the oxygen pressure remains at 20 Pa. Then turn on the radio - frequency power supply, keep the power at 60 W, ionize the oxygen to form plasma, and infiltrate it into the titanium nitride coating. The oxygen infiltration time is kept at 1 h to form a titanium oxynitride coating.

[0070] S4. Turn off the radio - frequency power supply switch, naturally cool to room temperature, and take out the sample from the chamber.

[0071] Example 3

[0072] As Figure 3 , a method for preparing a metal compound coating on the surface of a titanium bipolar plate, comprising the following steps:

[0073] S1. Surface pretreatment of the titanium substrate: Select a commercial TA1 titanium plate as the titanium substrate, and the commercial TA1 titanium plate is a titanium bipolar plate. Polish it with 1000 - 5000 - mesh SiC sandpaper to remove the oxide film on the surface of the titanium bipolar plate. Then, use diamond polishing paste with a particle size of 0.5 µm to polish the surface of the titanium substrate into a mirror state. Ultrasonically clean the polished titanium substrate with absolute ethanol for 30 min, and finally air - dry it naturally.

[0074] S2. Deposition of titanium nitride coating on the surface of the titanium substrate: Fix the air - dried titanium substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 −4After reaching 8 Pa, introduce high-purity nitrogen gas and adjust the nitrogen gas flow rate so that the nitrogen partial pressure remains at about 8 Pa; set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 400 mJ, and the number of pulses to 16,000 times. Then turn on the laser switch to start depositing the titanium nitride coating; a titanium bipolar plate with a titanium nitride coating on its surface is obtained.

[0075] S3. Oxygen infiltration process on the surface of the titanium nitride coating: Place the titanium bipolar plate with a titanium nitride coating on its surface prepared by the pulsed laser deposition process in the reaction chamber of the plasma chemical vapor deposition equipment. Raise the substrate temperature to 200 °C. When the chamber vacuum is lower than 1×10 −3 Pa, introduce oxygen into the chamber and adjust the oxygen flow rate so that the oxygen pressure remains at 25 Pa. Then turn on the radio frequency power supply and maintain the power at 60 W to ionize the oxygen to form a plasma, which infiltrates into the titanium nitride coating. Keep the oxygen infiltration time for 1 h to form a titanium oxynitride coating.

[0076] S4. Turn off the radio frequency power supply switch, naturally cool to room temperature, and take out the sample from the chamber.

[0077] Comparative Example 1

[0078] Use an untreated TA1 commercial titanium plate as the titanium bipolar plate sample before modification.

[0079] Comparative Example 2

[0080] A method for preparing a metal compound coating on the surface of a titanium bipolar plate, which is different from Example 1 in that the surface of the titanium nitride coating is not treated by the plasma oxygen infiltration process. The specific method includes the following steps:

[0081] S1. Surface pretreatment of the titanium substrate: Select a TA1 commercial titanium plate as the titanium substrate, and the TA1 commercial titanium plate is the titanium bipolar plate. Polish it with 1000-mesh to 5000-mesh SiC sandpaper to remove the oxide film on the surface of the titanium bipolar plate. Then, use diamond polishing paste with a particle size of 0.5 µm to polish the surface of the titanium substrate into a mirror state. Ultrasonically clean the polished titanium substrate with absolute ethanol for 30 min, and finally air dry it naturally.

[0082] S2. Deposition of a titanium nitride coating on the surface of the titanium substrate: Fix the air-dried titanium substrate on the sample stage and transfer it into the deposition chamber. Raise the substrate temperature to 400 °C. When the chamber vacuum is less than 2×10 −4 Pa, introduce high-purity nitrogen gas and adjust the nitrogen gas flow rate so that the nitrogen partial pressure remains at about 8 Pa; set the deposition target as a titanium nitride target with a purity of 99.9%, set the laser frequency to 8 Hz, the laser energy to 400 mJ, and the number of pulses to 16,000 times. Then turn on the laser switch to start depositing the titanium nitride coating; a titanium bipolar plate with a titanium nitride coating on its surface is obtained.

[0083] S3. Turn off the laser switch, allow it to cool naturally to room temperature, and remove the sample from the chamber.

[0084] Comparative Example 3

[0085] A method for preparing a metal compound coating on the surface of a titanium bipolar plate, which is different from Example 1 in that a titanium oxynitride coating is directly deposited on the surface of the titanium substrate. The specific method includes the following steps:

[0086] S1. Surface pretreatment of the titanium substrate: Select a commercial TA1 titanium plate as the titanium substrate, and the commercial TA1 titanium plate is a titanium bipolar plate. Use 1000 - 5000 mesh SiC sandpaper to polish and remove the oxide film on the surface of the titanium bipolar plate. Then, use diamond polishing paste with a particle size of 0.5 µm to polish the surface of the titanium substrate into a mirror state. Ultrasonically clean the polished titanium substrate with anhydrous ethanol for 30 minutes, and finally air dry it naturally.

[0087] S2. Deposition of the titanium oxynitride coating on the surface of the titanium substrate: Fix the air-dried titanium substrate on the sample stage and transfer it into the deposition chamber. Heat the substrate to 400 °C. After the chamber vacuum is less than 2×10 −4 Pa, introduce high-purity nitrogen and high-purity oxygen, and adjust the flow rates of nitrogen and oxygen so that the nitrogen partial pressure is maintained at about 8 Pa and the oxygen partial pressure is maintained at about 0.2 Pa. Set the deposition target as a 99.9% pure titanium nitride target, set the laser frequency to 8 Hz, the laser energy to 400 mJ, and the number of pulses to 16000 times. Turn on the laser to start depositing the titanium oxynitride coating; obtain a titanium bipolar plate with a titanium oxynitride coating on its surface.

[0088] S3. Turn off the laser switch, allow it to cool naturally to room temperature, and remove the sample from the chamber.

[0089] Use the samples modified in Examples 1 - 3 as Sample 1, Sample 2, and Sample 3. Use the sample before modification in Comparative Example 1 as Control Sample 1, the sample after modification in Comparative Example 2 as Control Sample 2, and the sample after modification in Comparative Example 3 as Control Sample 3. Conduct SEM and XPS analyses and corrosion resistance tests on the above samples to explore the surface morphologies and corrosion resistance properties of different samples.

[0090] Test 1: SEM and XPS analyses.

[0091] The English full name of SEM is Scanning Electron Microscope, and the Chinese name is scanning electron microscope. The English full name of XPS is X-ray Photoelectron Spectroscopy, and the Chinese name is X-ray photoelectron spectroscopy.

[0092] SEM analysis was carried out on the titanium oxynitride coating on the surface of the sample modified in Example 1, and the results are as Figure 2 shown. SEM analysis was carried out on the cross-section of the sample modified in Example 1, and the results are as Figure 1 shown. XPS depth analysis was carried out on the sample modified in Example 1, and the results are as Figure 4 shown.

[0093] As Figure 2 can be seen, the surface of the titanium oxynitride coating prepared in Example 1 is continuous and dense.

[0094] As Figure 1 can be seen, the titanium oxynitride coating prepared in Example 1 presents a columnar crystal structure with a thickness of about 300 nm.

[0095] Figure 4 shows the XPS depth analysis results of the sample modified in Example 1, where 0 min to 7 min is the XPS sputtering time. As Figure 4 can be seen, the titanium oxynitride coating prepared in Example 1 is a gradient coating, and its oxygen content changes with the coating thickness. The oxygen content on the coating surface is high, and the oxygen content decreases close to the titanium substrate.

[0096] Test 2: Corrosion resistance test.

[0097] Potentiodynamic polarization test: The samples before modification in Comparative Example 1, the samples after modification in Examples 1 to 3, and the samples after modification in Comparative Examples 2 to 3 were respectively subjected to potentiodynamic polarization test in 0.5 M H2SO4 + 0.2 ppm F - solution, and some test results are as Figure 5 and Table 1 shown. Generally, the more positive the corrosion potential and the smaller the corrosion current density, the smaller the corrosion rate of the material, that is, the stronger the corrosion resistance of the material.

[0098] Table 1 Influence of different oxygen pressures in the oxygen permeation process on the performance of the modified titanium bipolar plates

[0099]

[0100] Note: "-" indicates that the plasma oxygen permeation process was not carried out.

[0101] Figure 5 The results show that, after testing, in the PEMWE simulated working environment, the self-corrosion current density of the TA1 commercial titanium plate sample without any treatment in Comparative Example 1 is about 1.36×10 −4 A·cm −2 .

[0102] In the PEMWE simulated working environment, the corrosion current density of the sample modified in Example 1 decreased to 6.8×10− 8 A·cm −2 , the corrosion potential was -0.21 V. Compared with the sample before modification in Comparative Example 1, the corrosion resistance of the sample after modification in Example 1 was greatly improved.

[0103] Under the simulated working environment of PEMWE, the corrosion current density of the sample after modification in Comparative Example 2 decreased to 4.2×10 −7 A·cm −2 , the corrosion potential was -0.37 V. Compared with the sample before modification in Comparative Example 1, the corrosion resistance of the sample after modification in Comparative Example 2 was greatly improved. However, compared with Example 1, the corrosion current density of the sample after modification in Comparative Example 2 was still relatively high. This shows that the modification method in Example 1 is more effective in reducing the corrosion rate.

[0104] Under the simulated working environment of PEMWE, the corrosion current density of the sample after modification in Comparative Example 3 decreased to 5.2×10 −8 A·cm −2 , the corrosion potential was -0.30 V. Compared with the sample before modification in Comparative Example 1, the corrosion resistance of the sample after modification in Comparative Example 3 was greatly improved. The corrosion current density of Comparative Example 3 was similar to that of Example 1, indicating that they have similar effects in reducing the corrosion rate. However, considering the influence of the corrosion potential, that is, the more positive the corrosion potential, the better the corrosion resistance usually is. The corrosion potential of Example 1 was more positive than that of Comparative Example 3. Therefore, Example 1 had relatively better overall corrosion resistance.

[0105] In summary, compared with Comparative Example 2, the sample after modification in Example 1 showed better corrosion resistance in terms of both corrosion current density and corrosion potential. Compared with Comparative Example 3, although their corrosion current densities were similar, the corrosion potential of Example 1 was more positive, indicating that Example 1 had relatively better overall corrosion resistance. Thus, under the simulated working environment of PEMWE, the sample after modification in Example 1 had more excellent corrosion resistance than the samples after modification in Comparative Example 2 and Comparative Example 3. This may be because the modification method used in Example 1 is more effective in reducing the corrosion rate and increasing the corrosion potential.

[0106] Potentiostatic polarization test: The samples before modification in Comparative Example 1, the samples after modification in Comparative Example 2, and the samples after modification in Example 1 were respectively subjected to a potentiostatic polarization test at +2 V for 6 hours in a 0.5 M H2SO4 + 0.2 ppm F - solution, and the test results are as Figure 7 shown.

[0107] Figure 7 The results showed that at a working voltage of 2.0 V, the corrosion current density of the sample before modification in Comparative Example 1 was about 1×10−4 Acm −2 has poor corrosion resistance.

[0108] Compared with Comparative Example 1, the sample modified in Comparative Example 2 maintains a relatively smaller corrosion current density during the potentiostatic test in the PEMWE simulated working environment. Thus, it is proved that the sample modified in Comparative Example 2 has relatively better corrosion resistance and long-term working stability.

[0109] Compared with Comparative Example 1 and Comparative Example 2, the sample modified in Example 1 maintains a relatively smaller corrosion current density during the potentiostatic test in the PEMWE simulated working environment. Thus, it is proved that the sample modified in Example 1 has better corrosion resistance and long-term working stability compared with the sample before modification in Comparative Example 1 and the sample modified in Comparative Example 2. This shows that the modification method in Example 1 is more effective in improving corrosion resistance and long-term working stability.

[0110] Interfacial contact resistance test: To evaluate the interfacial contact resistance characteristics of different samples, the samples before modification in Comparative Example 1, the samples modified in Comparative Example 2 to Comparative Example 3, and the sample modified in Example 1 were respectively subjected to the interfacial contact resistance test between the sample and the gas diffusion layer, and the results are as Figure 6 shown in Table 1. The full English name of interfacial contact resistance is Interfacial Contact Resistance, abbreviated as ICR.

[0111] From Figure 6 the results, it shows that the ICR value of the sample before modification in Comparative Example 1 is 34 mΩ·cm 2 .

[0112] After the modification treatment, the ICR value of the sample modified in Comparative Example 2 decreased significantly, from 34 mΩ·cm 2 before modification to 5.4 mΩ·cm 2 . This shows that the modification treatment in Comparative Example 2 is effective in improving the interfacial contact performance.

[0113] However, the ICR value of the sample modified in Comparative Example 3 increased from 34 mΩ·cm 2 before modification to 57.6 mΩ·cm 2 . This shows that the modification treatment in Comparative Example 3 did not achieve the expected effect of reducing the ICR value, but instead increased it.

[0114] In contrast, the ICR value of the sample modified in Example 1 decreased from 34 mΩ·cm 2 before modification to 8.7 mΩ·cm 2。Although the reduction amplitude is not as large as that of Comparative Example 2, it also indicates that the modification treatment has a positive effect on improving the interface contact performance. Moreover, compared with the sample modified in Example 1, the ICR value of the sample modified in Comparative Example 3 increases significantly, further highlighting the effectiveness of the modification method in Example 1.

[0115] Based on the above analysis, compared with Comparative Examples 1 to 3, the sample modified in Example 1 of the present invention shows a relatively significant effect of reducing the ICR value. This indicates that the modification method adopted in Example 1 is more effective in improving the contact performance between the sample and the gas diffusion layer or other relevant interfaces.

[0116] It should be noted that although the modification effect of Comparative Example 2 is also very significant, compared with Example 1, the corrosion current density of the sample modified in Comparative Example 2 is still relatively high. Thus, it shows that the modification treatment method in Example 1 is more effective in reducing the corrosion rate. And Figure 7 The results further show that compared with Comparative Example 2, the sample modified in Example 1 has better corrosion resistance and long-term working stability. This further proves that compared with Comparative Example 2, the modification treatment method in Example 1 is more effective in improving corrosion resistance and long-term working stability.

[0117] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a metal compound coating, characterized in that: The metal compound coating is used to cover the surface of the titanium bipolar plate of the water electrolysis device. The preparation method of the metal compound coating comprises the following steps: A titanium bipolar plate of a water electrolysis device is used as a substrate, and a titanium nitride coating is deposited on the surface of the substrate by a pulsed laser deposition process; then, a plasma surface oxygen permeation process is used to oxygenate the titanium nitride coating at 200° C. to form a titanium oxynitride coating with a gradient oxygen content; the thickness of the titanium oxynitride coating is 240 nm to 300 nm; The conditions of the plasma surface oxygen permeation process are: power of 60W, gas pressure of the reaction chamber of 15Pa to 30Pa, and oxygen permeation time of 1h to 3h.

2. The method for preparing the metal compound coating according to claim 1, characterized in that: The oxygen content of the titanium oxynitride coating decreases gradually along the thickness direction as the titanium oxynitride coating approaches the substrate.

3. The method for preparing the metal compound coating according to claim 1, characterized in that: A method for depositing a titanium nitride coating on a substrate surface using pulsed laser deposition technology comprises the following steps: The pulsed laser deposition process was used, with TiN target as the target material and nitrogen as the working gas. -4 Nitrogen gas is introduced after 400 Pa to form a titanium nitride coating on the surface of the substrate.

4. The method for preparing the metal compound coating according to claim 3, characterized in that: The conditions for the pulsed laser deposition process are: The pulse frequency is 8 Hz to 10 Hz, the laser energy is 400 mJ to 450 mJ, the gas pressure of the reaction chamber is 8 Pa to 10 Pa, the deposition temperature is 400° C. to 450° C., and the number of pulse depositions is 12,000 to 16,000 times.

5. The method for preparing the metal compound coating according to claim 1, characterized in that: A method for forming a titanium oxynitride coating with a gradient oxygen content comprises the following steps: A plasma surface oxygen permeation process is adopted to introduce oxygen, ionize the oxygen to form oxygen plasma, and then permeate into the titanium nitride coating to form a titanium oxynitride coating with a gradient oxygen content.

6. A metal compound coating, characterized in that: The method is prepared by any one of claims 1 to 5.

7. A modified bipolar plate, characterized in that: It comprises a substrate and a metal compound coating, wherein the substrate is a titanium bipolar plate of a water electrolysis device, and the metal compound coating is the metal compound coating according to claim 6.

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